The invention relates to a cylinder head for internal combustion engines, especially diesel engines with direct fuel injection.
In high-speed diesel engines with direct fuel injection, such as mostly used in passenger vehicles and trucks, spin flow in the combustion chamber about the longitudinal axis of each cylinder is needed in order to achieve proper mixing and homogenization. Spin can be induced in combustion air either through a suitable orientation of the inlet channel or by means of an eccentric chamfer provided at the valve seat of the inlet valve.
GB-PS 1,568,302 discloses an internal combustion engine wherein the valves are arranged V-like in the cylinder head and are given an extremely pronounced tilt so that the valves, during movement thereof toward their open position, will open early in a region adjacent the cylinder wall but, due to the inclined disposition of the valve seats, will open in the region proximate to the longitudinal axis of the cylinder only near the end of the maximal valve stroke. With this conventional arrangement, combustion air entering the combustion chamber through the inlet valve is directed to flow along the wall of the cylinder parallel to the longitudinal axis thereof in order to prevent combustion air exiting the inlet valve from being short-circuited to the adjacent exhaust valve.
This known arrangement requires an extremely pronounced valve tilt of about 45 degrees, with respect to the longitudinal cylinder axis, in order to obtain the desired result, but in many engines such an extreme valve tilt cannot be realized due to space restrictions and other conditions arising from the particular construction of the engine involved. This holds true particularly of engines utilizing two inlet valves per cylinder.
DD 234 998 A3 discloses a cylinder head with a spin-inducing inlet channel for use in diesel engines employing direct fuel injection. The intent of this prior disclosure is to influence the inherent spin-inducing characteristics of the inlet channel in a manner such that the spin rate will remain constant throughout a valve stroke, and also that the maximal spin rate can be changed. To this end, this prior disclosure proposes to provide a crescent-shaped chamfer extending eccentrically, with respect to the longitudinal axis of the inlet valve, approximately halfway around the valve; this prior disclosure proposes also to provide a small concentric chamfer for the remainder of the valve's circumference.
With this known arrangement, a uniform gap is formed all around the inlet valve during the initial phase of a valve stroke so that, initially, the same amount of combustion air will flow through the valve throughout its circumference. Later in the valve stroke, a larger gap is formed at the eccentric chamfer but this will come too late to produce enough spin.
U.S. Pat. No. 2,768,618 discloses a cylinder head for an internal combustion engine including an inlet valve which is tilted relative to the longitudinal axis of the cylinder such that one section of its valve seat is near the contour defining the combustion chamber, whereas another section of the valve seat lies farther inward of the cylinder head. As a result, combustion air will tend, especially during short valve strokes, to enter the combustion chamber mainly through the section of the valve seat which is nearer the combustion chamber, thereby producing spin flow about the longitudinal axis of the cylinder.
With this known arrangement, the degree of spin obtainable depends essentially upon the tilt of the inlet valve; i.e., if there is little tilt, combustion air will enter the combustion chamber in the preferred direction only during a short part of the valve movement so that no spin or not enough spin may be produced. Of course, the degree to which an inlet valve can be tilted depends usually upon conditions dictated by the arrangement and disposition of the inlet conduits, camshaft, coolant channels, and the like.
DE-PS 478,415 discloses a cylinder head including an inlet valve wherein a chamfer for imparting to combustion air entering the cylinder a preferred direction is provided at the valve seat of the inlet valve on a side thereof distant from an inlet channel.
The chamfer in this known arrangement performs its desired function owing to the fact that, during a short valve stroke, the flow cross-sectional area is substantially larger at the chamfer than in the valve region where there is no chamfer. However, the teachings of this earlier disclosure cannot be applied to cylinder heads having two inlet valves since the combustion air entering the cylinder from the different chamfer regions would spin in opposite directions so that the flow vectors of the two air streams would essentially cancel each other.
It is the principal objective of the present invention to provide an improved cylinder head with two inlet valves including spin-inducing means for substantially enhancing spin flow about the longitudinal axis of a cylinder independently of valve tilt.